Dissociated fetal mouse and rat brain and spinal cord are grown on plastic or collagen coated tissue culture vessels. Intracellular microelectrode techniques and microiontophoresis are used to assay surface membrane properties of chemical and electrical excitability. We have found that the presence of glycine chronically in the culture medium prevents formation of inhibitory synapses between cultured spinal cord cells. Inhibitory synapses do form between brain cells grown in glycine containing medium. Glycine is probably the inhibitory transmitter in the spinal cord, but in the brain, many inhibitory synapses are not glycinergic. The blocking effect of glycine thus appears to be specific to glycine mediated synaptic connections. Spinal cord neurons exhibit an electrogenic sodium pump which is active even in quiescent cells and which is further activated by procedures that increase the intracellular sodium concentration. Experiments have been initiated on the membrane effects of a variety of oligopeptides, including substance P and thyrotropin releasing factors. It appears that some of the active peptides of importance in the endocrine systems have neuronal actions as well. Pentobarbital decreases the glutamate responses and prolongs and alters the configuration of the GABA response. Other anesthetic agents tested only depressed the glutamate responses.